1. Technical Field of the Invention
The present invention concerns an inverter transformer and an inverter circuit used in a cold cathode tube light for an LCD (liquid crystal display) backlight, etc.
2. Related Technology
Conventionally, cold cathode tubes are employed in LCD backlights. With the aim of devising more efficient and smaller-sized lighting, a separate excitation drive circuit employing an IC is used. This separate excitation drive circuit uses, for example, the resonance image of the floating capacity resulting from the cold cathode tube, which serves as a charge, and the device in which it is mounted, and the leak inductance of a driving step-up transformer (inverter transformer). This resonance image generates high voltage. Illumination occurs by applying this high voltage to the aforementioned cold cathode tube.
When the cold cathode tube in the aforementioned circuit is damaged or when there is no contact between the cold cathode tube and the step-up transformer, extremely high voltage is output continuously from the step-up transformer. This has caused such problems as step-up transformer breakage, driving circuit breakage, and so on.
The type of circuit structure depicted in FIG. 8, for example, is used to resolve the aforementioned problems. Provided on the secondary side of the step-up transformer (100) are two in-line condensers (C1), (C2). Voltage divided by these condensers (C1), (C2) is supplied to IC (120) and abnormalities are detected. If an abnormality is detected, circuit protection has been devised in that the switch signal supplied by the IC (120) to the transistor TR base is interrupted.
However, in a circuit structured in the manner described above, the condensers (C1), (C2) serving as circuits to detect abnormalities are directly connected to the step-up transformer (100), a high-voltage output component. Consequently, because the aforementioned condensers (C1), (C2) are small capacity, a special high-voltage resistant condenser that can resist high voltage is required (several pF high-voltage ceramic condenser). This is one aspect that contributes to increasing the cost of the apparatus.
Furthermore, when abnormalities such as breakage of the step-up transformer (100) and cold cathode tube (110), etc. occur, the circuit components that safeguard the drive circuit and the step-up circuit (100) comprising the IC (120) and the transistor (TR) are concentrated on the output side of the step-up transformer (100). Since the output side of the step-up transformer (100) outputs several hundred to several thousand volts of high voltage, the components must be physically separated, thus causing the problem of increasing the circuit mounting surface area.
The present invention was created to resolve these sorts of problems found in conventional inverter circuits. Thus, an objective of the invention is to provide an inverter circuit that does not require special high-cost components and whereby protection appropriate to the circuit and the rising-voltage transformer can be devised. In the present invention, moreover, an objective is to provide an inverter circuit without a large mounting surface area in that there is no need to place components on the high output side of the step-up transformer. A further objective of the present invention is to provide an inverter transformer to use in the aforementioned inverter circuit.